I had started learning c++ in which I came to know that if there is a virtual function in the base class then the vptr is created only in the base class & once the object of the class is created at run time then the vptr is set to point to the vtable of the class whose object is created.
But, when I printed the size of the empty class with virtual function then it comes out to be 8 bytes.
#include <bits/stdc++.h>
#include <iostream>
using namespace std;
#pragma pack(1)
class A{
public:
virtual void display(){
cout<<"A Class"<<endl;
}
};
class B: public A{
public:
void display(){
cout<<"A Class"<<endl;
}
void show(){
cout<<"B Class"<<endl;
}
};
int main()
{
cout<<sizeof(A)<<" "<<sizeof(B);//8 8
return 0;
}
Above is the code which I ran.
My Question is if vptr is created when the object is created at run time then why here size comes out to be 8 bytes even if the object of the class has not been created yet.
Also one more question that comes out is
#include <bits/stdc++.h>
#include <iostream>
using namespace std;
#pragma pack(1)
class A{
public:
virtual void display(){
cout<<"A Class"<<endl;
}
};
class B: public A{
public:
};
int main()
{
cout<<sizeof(A)<<" "<<sizeof(B);
return 0;
}
Here if I leave class B as empty then total how many vtables will be created here ?
I tried using std::is_polymorphic::value for verifying if vtable is created in the table or not but, I am not sure of this function.
